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pages/总复习2023t1.md
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@ -1006,29 +1006,30 @@
- The instances of a potential subclass participate in a relationship unique to that subclass. - The instances of a potential subclass participate in a relationship unique to that subclass.
- DONE Block 3 - DONE Block 3
- DONE DB transaction management - DONE DB transaction management
- anomalies - LATER anomalies
- DONE ACID (Atomicity, Consistency, Isolation, Durability): A set of properties that guarantee the reliability and integrity of database transactions. #flashcard - DONE Deadlock and how it can be resolved. #flashcard
- Atomicity: :-> The property that ensures a transaction is treated as a single, indivisible unit of work. It either executes all its operations successfully or rolls back to the initial state if any operation fails.
- Consistency: :-> The property that ensures a transaction transforms the database from one consistent state to another consistent state. It maintains data integrity and adheres to defined business rules.
- Isolation: :-> The property that ensures concurrent transactions do not interfere with each other. Each transaction operates in isolation until it completes, preventing interference or conflicts.
- Durability: :-> The property that ensures committed changes made by a transaction are permanently saved and will survive any subsequent system failures or crashes.
- DONE Concurrency control
- DONE Meaning of serialisability.
- DONE How locking can ensure serialisability.
- Locking achieves serializability by using locks to control access to
shared resources (e.g., database objects like tables or rows) and
prevent conflicts between concurrent transactions.
- DONE 2PL
- In the 2PL protocol, transactions acquire and release locks on database
objects (e.g., tables, rows) in two distinct phases: the growing phase
and the shrinking phase.
- DONE Deadlock and how it can be resolved.
- A deadlock is a situation in which two or more transactions are unable - A deadlock is a situation in which two or more transactions are unable
to proceed because each is waiting for a resource held by the other, to proceed because each is waiting for a resource held by the other,
resulting in a circular dependency and a system halt. It is a form of resulting in a circular dependency and a system halt. It is a form of
resource contention that can occur in concurrent systems, including resource contention that can occur in concurrent systems, including
database management systems. database management systems.
- DONE How timestamping can ensure serialisability. - DONE ACID (Atomicity, Consistency, Isolation, Durability): A set of properties that guarantee the reliability and integrity of database transactions. #flashcard
collapsed:: true
- Atomicity: :-> The property that ensures a transaction is treated as a single, indivisible unit of work. It either executes all its operations successfully or rolls back to the initial state if any operation fails.
- Consistency: :-> The property that ensures a transaction transforms the database from one consistent state to another consistent state. It maintains data integrity and adheres to defined business rules.
- Isolation: :-> The property that ensures concurrent transactions do not interfere with each other. Each transaction operates in isolation until it completes, preventing interference or conflicts.
- Durability: :-> The property that ensures committed changes made by a transaction are permanently saved and will survive any subsequent system failures or crashes.
- DONE Concurrency control
- LATER Meaning of serialisability.
- DONE How locking can ensure serialisability. #flashcard
- Locking achieves serializability by using locks to control access to
shared resources (e.g., database objects like tables or rows) and
prevent conflicts between concurrent transactions.
- DONE 2PL #flashcard
- In the 2PL protocol, transactions acquire and release locks on database
objects (e.g., tables, rows) in two distinct phases: the growing phase
and the shrinking phase.
- DONE How timestamping can ensure serialisability. #flashcard
- By using transaction timestamps and enforcing the read and write - By using transaction timestamps and enforcing the read and write
validation checks, concurrency control mechanisms can ensure that validation checks, concurrency control mechanisms can ensure that
transactions are executed in a way that maintains data consistency and transactions are executed in a way that maintains data consistency and
@ -1049,7 +1050,7 @@
- Checkpoint records. - Checkpoint records.
- Often used for other purposes (for example, auditing). - Often used for other purposes (for example, auditing).
- For autiding - For autiding
- DONE Purpose of checkpointing. - DONE Purpose of checkpointing. #flashcard
- When failure occurs, redo all transactions that - When failure occurs, redo all transactions that
committed since the checkpoint and undo all committed since the checkpoint and undo all
transactions active at time of crash. transactions active at time of crash.